Propeller pitch stop system



Sept. 15, 1953 M. E. LoNGFELLow 2,652,122

PROPELLER FITCH STOP SYSTEM Filed May 3, 1950 3 Sheets--Sheei'l l FNVENTOR gfflhglnngfH/Zm mlm/u', 9. M5L, ATTORNEY Sept. 15, 1953 M. E. LoNGFELLow 2,652,122

PROPELLER FITCH STOP SYSTEM Filed May 5, 1950 3 Sheec--Sheet 2 Ta Peeps/.LER C oA/Tez.

ELA'Y Box E a. 9g INVENTOR ATTORN EY Sept. 15, 1953 M. E. LoNGFELLow PROPELLER PITCH STOP SYSTEM 3 Sheets-Sheet 5 Filed May 5, 1950 Q O l.) Q

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INVENTOR IMQ/wh ATTORNEY Patented Sept. 15, 1953 U N ITED PATENT Q'FEF ICE Melvin Longfellow, Manchester, Conn., as-

.signor .to :United Aircraft .(lorporation, East Hartford, Conn.,.a corporation .of Delaware Application May l3, 1950, "SBralI'TNO. 159;736

This invention relates to improvements c-in :airalraft propellers :and :more specifically to variable '.pitch `propellers having -fimproved .control means ftherefor.

'It is .an object @of .this yinvention `.to .provide-.an improved pitch control and operating mecha- .nism .for .variable pitch l.'propellers.

Another :oblject of #this invention :is to `provide 1a propeller :of Vthe `rtype `described .having pitch `vary-ing mechanism "including ycontrol means therefor :wherein the fpitch of the fbladespan .be `selectively ilocked .against fpitch variation.

Azfurthervob'ject Aof this `invention -is Eto fprovide fa variable pitchrpropellerlhaving -a control=mech :anism :thereforwhereby :the blades can be 'locked sagainst pitch variation iby mechanism directly engaging the iblades Yand whereby -the blades can =be further locked against pitch change by means 'of `locking mechanism fwhich forms a Tpart of the above-'mentioned :control mechanism.

A still lfurther object -o'f lthis *invention is to provide =a propeller'pitch lock .system Yof v1the ltype ldescribed l.wherein ithe propeller lcontrol system comprises a plurality of control lelements rfor `simultaneously operating .the pitch loc-ks W-hile -provid-ing ypitch limit `units for -a constant speed range, la starting setting, 'feathering and reve-rsing and afurther providing 'manual Ilock :controls ltherefor.

.Another object Aof this invention is to provide' =a lock pitch unit -for Ja propeller pitch ychanging lcontrol ysystem IWhich Ais 4capable `of 'locking the blades Iagainst Apitch -change selectively in `any one -clirection and simultaneously 4against :movement in bot-h pitch changing direct-ions.

These and other objects will become nreadily .apparent from the ifollovv'insr detailed ldescription of the `accompanying drawings inwhiclr:

Fig. 21 is a schematic `illustredzion cf a propeller "and associated Agea-r train I'for transmitting control'lng-movements'lrom the control system to Athe hub carried pitch changing mechanism.

Fig. 2 :is a schematic illustration of ythe propeller `control system yof this invention with the )elements'arransed :as Iacontinuity 'of Fig. 41.

"FigJZa is a detailed Across-sectional fv-iew of the A.pitch 'lock unit.

1Fig.'3 isf=an^electrical schematic diagram yof the propeller 4corrtrol system.

Referring -to flli'g. i, a `propr-311er yis illustrated Ias bein-g operatively 'connected by -a driving element or rear yIl! which may `form a part of a 'turbine or .reciprocating piston power v.plant and Awhich also serves to Adrive a 'taohom-eter .generator I2 ywhich 1vinftur-n transmits electrical energy to -a-n .2 electronic `governor schematically shown fat t4. Ehe electronic fgoyernor Vin turn 'bot-h Ireceives .and transmits Lelectrical signals :to the :propeller .conttrol system as will become :apparent Vhereina'ter.

The propeller illustrated herein comprises a hub 20 which may have a :plurality .o'f radially v`extending variable ..pitch blades '.22 `mounted `therein `'with teach fof the :blades having huid .operated--vaneimotors '.2 4 mounted mithin the :Shanks thereof. The vane motors 24 respond \to high 'pressure Aiuid toa/ary ath-e `:pitch of thefblades in Aa, 'low Apitch `-or high pitch direction, las .indicated by the arrows, .it bingrnoted .that the letters LP and HP are :used -in'the :drawings `4tto .indicate .said pitch :directions respectively.

'The-:propeller hub 2,0 carries the .entire .xpitch #actuating Lmechanism 'internally thereof including ran integral ihyd-raulic reservoir, `the :actual construction :of which is Imore :clearly 'illustrated :and described incopending applicationeriallNo. '154,857,1ledApri118, 21950, by Arthurit. Allen, l-r.

f A pressurized sump 30 fis provided Sfor f-supplying lhuid to la high-#pressure main pump 432 `and a Jstand-by :pump "34 -by means of hydraulic 'lines yf36 fand -3^8, respectively. The sump 310 is pressurized -to .some nominal value by means of 'a scavenge pump 4-0 which receives uid from an oi-l Acharnber (not illustrated) lunder atmos- `pherie pressure. vsump 30 is maintained at -this predetermined normalpressure by means of asumir) relief valve 42 which .dumps relieved huid back l'into @the above-mentioned chamber which lis `under atmospheric pressure. High pressure "fluid from the pumps 32 'and 234 is directed to a distributor I-yalve generally indicated lat '4B 1which controllably directs this high vpressure iiuid `vvia the lines "48 or 50 `to either side of the vane-motors 2li for-varyingthefpitch rof-theblaci1es v2. VSince lthe capacity lof the Kmain -pump 4'32 is suliicient for normal 'pitch chang-ins movements, the output of the stand-by pu-mp 311 -is Adirected from rthe line 52 'around the land A54 of the -dis- 'tributorvalve '46 `and lthen to the port -55 of the valve to a central Idrain passage 58 therein. When the vdemand `for lpitch changing movements iis hie-h, as reflected by large movements rof the cdistributor valve, the land 54 will close *oif the incoming Vhuid from the passage 52 so l'that `the A pressure Iin 'the 'passage 42 will immediately 4build up, sufficiently -to open the 'check valve "5B 4so that v'an Aadditional volume of fluid Will 'loe available for pitch changing movement to 'supplement the 'flow ofhigh pressure uid coming *from the main `pump 32 via the line '62.

The central portion 'of the distributor valve 46 is actuated in reciprocating motion by means of a drive nut 'I0 engaging the worm 'I2 carried by the central valve portion. A follow-up gear 'I4 is splined to the shaft of the worm 12 so that by means of the gear train 'i6 and the associated shaft I8 the valve central portion will be repositioned when the blade interconnecting gear 80 is rotated by the gear segments 82 (carried by the blade 22) during pitch changing movements of the blades.

A positive ratchet type pitch lock 90 is provided for automatically locking the blades against pitch changing movements in a low pitch direction in the event of failure of hydraulic pressure in the system. A spring 92 biases a pitch lock piston 94 toward a lock position while iiuid under pressure flowing via the line 96 forces the piston 94 toward an unlocked position. The uid under pressure in the line 96 is fed via a passage which surrounds the follow-up shaft 18 and normally communicates with the central drain chamber of the distributor valve Via a port 98, the land adjacent the port 98 normally permitting fluid communication to the pitch lock piston. The drain pressure within the central chamber 58 of the s distributor valve is maintained at some predetermined value slightly above the pressure of the sump 30 by means of a pitch lock relief valve which is illustrated in the end of the distributor valve 46.

The pitch lock system shown herein is more fully described and claimed in co-pending patent application Serial No. 129,082, led November 23, 1949, by Erle Martin and Thomas B. Rhines.

The propeller parts described thus far are con- 1 tained within, or form a part of, the rotatable hub portion of the propeller assembly and the mechanism hereinafter described is carried in stationary housing held xed relative to the associated power plant. To this end, then, a pair of integral gears I0 and I I2 are normally fixed so that during propeller rotation the gears I I4 and I6 which engage the gear I I0 will revolve thereabout and in so doing will provide a rotational drive for the main pump 32 and the stand-by pump 34. The scavenge pump 40 contained within the propeller hub will likewise be drivingly rotated through its gear IIB which also engages the normally stationary gear ||0. A

second pair of integral gears |20 and |22 are, dur-:f

connected for rotation with the propeller and its drive shaft. The gear |20 (which normally rotates at propeller speed) engages a distributor valve driving gear which is fixed to the distributor valve driving nut 10. It is then apparent that during an on-speed condition with the gears |20 and |22 rotating at a speed identical to propeller rotation, the distributor valve drive gear |30 will remain stationary so as not to disturb the setting of the distributor valve 46.

Gears |20 and |22 preferably are mounted immediately adjacent the propeller shaft internally of the normally stationary gear I|0 so as to eliminate high relative rotational speeds between gears |20 and |22 and the propeller shaft. This holds true because the gears I I0, I I2 will be carried remote from the gears |20, |22 by the control housing.

The epicyclc gear train |26 comprises a shaft on which all of the gears thereon are mounted freely. The gears |42 and |44 are connected together for simultaneous rotation, as are also the gears |46 and |48. The gears |44 and |48 may be considered as sun gears and are respectively engaged with the planet gears |50 and |52 which are carried by, and fixed to, a common shaft |54 freely mounted in the gear |56 which forms the planetary cage. A control gear |60 is fixed to a shaft |62 and is driven via the bevel gears |64 by the servo control output shaft |68. During an on-speed condition then, with the servo control output shaft |68 stationary, the control gear |60 will also remain stationary and likewise the planetary cage or gear |56 will also remain stationary. Under these conditions, then with the gear |28 rotating at propeller speed and since it engages the gear |42, a driving train will be provided through the sun gear |44, the planetary pinions |50 and |52, through the gears |48 and |46 and finally to the gears |22 and |20. This driving connection just described in effect then provides a, simple step-up, step-down gear train which results in driving the gears |20 and |22 at a speed identical to propeller rotational speed so that no resultant movement of the propeller distributor valve and hence no blade angle change will obtain.

It will then be apparent that in the event the servo control output shaft is rotated to call for an increasing or decreasing pitch change, the bevel gears |64 will rotate the control gear |60 and the planetary cage |56 so that the planetary pinions |50 and |52 will revolve about their respective sun gears |44 and |46 so as to vary the resulting driven speed of the gear |46 and the gears |22 and |20. This variation in speed of the gears |20 and |22 then represents an increase or decrease, as the case may be, from the rotational speed of the propeller so that relative movement in either direction is obtained between the gear |20 and the distributor valve drive gear |30. As a result, the distributor valve drive nut will cause a subsequent reciprocating movement in the distributor valve so as to vary the pitch of the propeller blades.

A second planetary gear cluster has also been provided as an operative connection between the propeller and the servo control input shaft |82 whose purpose will be described hereinafter. The gear cluster |80 comprises a normally driven gear |84 which engages the gear |28 and, therefore, is driven in timed relation to, and by the rotation of, a propeller. A sun gear |86 is driven by the gear |84 and engages a planetary pinion |88 which in turn meshes with the internal teeth of the ring gear |90. Since the ring gear meshes with the normally fixed gear ||2 through a reversing gear |92, it also will be held stationary during normal operation. As a result, the planetary pinion |88 will revolve about the sun gear |86 and thereby through its shaft |96 the bevel gears |88 and the servo control input shaft |82 will be rotated.

As previously described, the normally stationary gears ||0 and ||2 provide for operation of the hub carried pumps when the propeller is rotating. It is then apparent that some means is necessary to operate these pumps so that high pressure fluid for propeller pitch change is available when the propeller is not rotating, as for example, when it is desired to unfeather the propeller in flight or on4 the ground. To this end au auxiliary motor is provided with a worm drive 2|6 for rotating the normally stationary gears I I2 and 0 through the interconnecting spiral gear 2|2. A ratchet mechanism is attached to to the servomotor and to isolate the topping governor from thesystem to prevent it from calling for a pitch change in the wrong sense if an overspeed occurs in reverse. The by-passing is accomplished by unseating the ball check 280 in the reverse solenoid 236. With the ball check unseated, high pressure oil, which in metered form is leaving the pilot valve 230 into the line 240, will be permitted to flow via the line 232 through the normally closed chamber 234 of the reversing solenoid Valve 236 past the open ball check 280 and into the chamber 246 of the valve from whence it may flow directly to chamber 248 of the servomotor.

For feathering, the proportional solenoid is energized in the high pitch direction which drains chamber 248 and allows direct high pressure oil to flow to the chamber 228 to move the servomotor to the extreme high pitch position. In

other words, by energizing the proportional solenoid in an extreme high pitch direction causes it to no longer meter oil into the line 240 so that no pressure whatsoever is admitted to the low pitch side of the servomotor.

Since the position of the servo controller output shaft is a direct indication of propeller blade angle, a. pitch stop cam mechanism 290 is connected directly to the shaft 168 by means of gears 292. The cam mechanism consists of five adjustable cams to provide a normal high pitch limit, a normal low pitch limit, a reverse limit, a feather limit and a starting limit which would correspond to an approximate zero pitch blade angle. Each of the individual cam elements are arranged to selectively trip electrical limit switches 294 which in turn disable the desired portion of the electrical system contained in the propeller control relay box.

In order to sensitize the operation of the electronic governor and its output signal to the propeller solenoid, a feedback potentiometer has its moveable element connected to the shaft 296 which carries the pitch stop cam mechanism 29B. Hence, the movements of the servo output shaft |68 will provide a simultaneous variation of potential output of the potentiometer which output is fed back as a signal to the electronic governor to provide in effect anticipator or followup signal.

Fig. 3 illustrates the various electrical units' ments are also shown diagrammatically herein,

as for example the auxiliary motor and lock pitch solenoids. For convenience, the specific electrical wire connections are not enumerated throughout. For convenience of description instead, the general operation of each of these switches and the result produced on the operating electrical elements is generally described. As previously mentioned, one limit switch is provided for each propeller stop position and these in addition to the other electrically responsive elements are diagrammatically indicated along the right hand side of Fig. 3.

During normal governing operation the low and high pitch lock solenoids are held energized through the normal low and normal high pitch limit switches. Then, if for any reason the governor servo system (Fig. 2) moves to a lower pitch than the setting of the normal low pitch limit switch, the associated cam will trip this switch to open the circuit to the low pitch solenoid of the pitch lock and prevent the output shaft |68 of the servo unit from moving any further toward low pitch. Following this, should. the governor servo system move again toward high pitch the output shaft |68 will ratchet away from its locked position until the low pitch limit switch is returnedl to normal (as for example by spring loading). The low pitch solenoid 212 of the pitch lock unit will again be energized to disengage the lock. The normal high pitch limit switch will lock the servo output shaft in a similar manner by de-energizing the high pitch solenoid 214 of the pitch lock unit.

In the event that the feather switch is operated, a plurality of circuits are completed or closed. First, the holding coil 36B of the feathering switch is energized under the control of the closed feather limit switch. Second, the increase pitch relay is energized so that it opens the governor circuit and simultaneously applies battery current to the governor proportional solenoid with a polarity to cause the governor servo system to operate in a high pitch direction. Third, the high pitch solenoid 214 of the pitch lock unit is held energized (unlocked position) independently of the normal low pitch limit switch. Fourth, the relay 3H) is energized so that the switch 312 is closed to provide current to the auxiliary motor. Following this, the servo output shaft |68 actuates the distributor valve-within the propeller hub to move the blades toward a feather position, keeping in mind that the position of the servo output shaft l is a direct indication of blade pitch position when the servo if output shaft has moved to the-feather position.

The feathering cam will actuate the feather limit switch toward an open position to open the holding coil 360 of the feathering switch which will cause the switch to return to normal position. At the same time the high pitch solenoid 214 of the pitch lock unit is de-energized so that its corresponding spring 216 (Fig. 2) will engage the lock preventing further movement of the servo output shaft toward a higher pitch, i. e., beyond feathering. As a precautionary safety measure, it is possible to override the deenergizing operation of the feather limit switch by further manual operation of the feathering switch in a feathering direction.

To unfeather the propeller the unfeathering switch is moved toward the UF position which energizes the unfeather relay via the line 320; and since in moving to the feathered position the normal high pitch limit switch had been moved to the dotted line position, the relay 3|!) (for the auxiliary motor) is energized also as follows. Battery current ows from the lock pitch switch via the line 324, through the high pitch limit switch (in dotted position), through line 326 and the line 328 adjacent the unfeather relay switch (which is now closed) and finally to line 33D and the relay 3I0 to energize the auxiliary motor. Thus it will be apparent that when the servo shaft returns to the high pitch limit switch setting this switch will return to its normal (full line) position to de-energize the auxiliary motor.

At the same time that current is flowing from the lock pitch switch (Via line 324) as described above (for energizing the auxiliary motor), current will also flow through the normal low pitch limit switch via line 334 back through connection 336 and then via line 338 to energize the low pitch lock solenoid 212 toward an unlock position thus permitting movement toward low pitch (unfeather).

comprising a source of servo power, a servomotor and a second control means connected to said servo source of power for controlling said servomotor including operative connections to said governing means, means driven by said servomotor having operative connections to said first controlling means, means for locking said driven means including an electrically actuated mechanical lock, and pitch stop means including cam mechanism operatively connected to said driven means and electrical elements actuated by said cam mechanism and an electrical network for selectively engaging and disengaging said lock means including electrical connectors bridging said stop means and said lock.

4. An aircraft propeller according to claim 3 wherein said network includes manually operated electricalmeans for engaging and disengaging said locking means.

5. In an aircraft propeller comprising variable pitch blades, means for varying the pitch of said blades through positive and negative pitch ranges including a source of power therefor, a rst controlling means operatively connected to said pitch varying means for controlling said pitch varying means, means for governing said first controlling means, a servo system comprising a source of servo power, a servomotor and a second control means operatively connected to said servo source of power for controlling said servomotor including operative connections to said governing means, means driven by said servomotor having operative connections to said rst controlling means, means for locking said driven means including an electrically actuated mechanical lock, cam means operable in response to movements of said driven means, an electrical system comprising limit switches and manually operated switches, said limit switches being operated by said cam means, and electrical means for selectively disengaging said locking units in response to actuation of said manual switches and for selectively engaging said locking units in response to operation of said limit switches including electrical connections between said switches and said lock units.

6. In an aircraft propeller according to claim 5 including means for automatically engaging said lock units selectively in response to failure of said servo power and electrical power including operative connnections to said sources of power.

7. In an aircraft propeller comprising variable pitch blades, means for varying the pitch of said blades through positive and negative pitch ranges including a source of power therefor, a iirst controlling means operatively connected to said pitch varying means for controlling said pitch varying means, means for governing said first controlling means, a servo system comprising a source of servo power, a servomotor and a second control means operatively connected to said servo source of power for controlling said servomotor including operative connections to said governing means, means driven by said servomotor having operative connections to said rst controlling means, means for locking said driven means including an electrically actuated mechanical lock, said lock being movable to lock said driven means against movement in any of two pitch changing directions, an electrical system comprising a feathering switch electrically connected to said operative connections for disconecting said connections from said gov- -erning means and including operative connections to said locking means for simultaneously disengaging said lock to permit movement of said driven means in one of said directions, and a feathering limit switch operative in response to a predetermined movement of said driven means for simultaneously engaging said lock means and disabling said feathering switch.

8. In an aircraft propeller comprising variable pitch blades, means for varying the pitch of said blades through positive and negative pitch ranges including a source of power therefor, a rst controlling means operatively connected to said pitch varying means for controlling said pitch varying means, means for governing said rst controlling means, a servo system comprising a source of servo power, a servomotor and a second control means operatively connected to said servo source of power for controlling said servomotor including operative connections to said governing means, means driven by said servomotor having operative connections to said rst controlling means, means for locking said driven means including an electrically actuated mechanical lock, said lock being movable to lock said driven means against movement in any of two pitch changing directions, and an electrical system comprising a feathering switch electrically connected to said operative connections for disconnecting said connections from said governing means and including operative connections to said locking means for simultaneously disengaging said lock to permit movement of said driven means in one of said directions.

9. In an aircraft propeller comprising variable pitch blades, means for varying the pitch of said blades through positive and negative pitch ranges including a source of power therefor, a rst controlling means operatively connected to said pitch varying means for controlling said pitch varying means, means for governing said first controlling means, a servo system comprising a source of servo power, a servomotor, and a second control means operatively connected to said servo source of power for controlling said servomotor including operative connections to said governing means, means driven by said servomotor having operative connections to said first controlling means, means for locking said driven means including an electrically actuated mechanical lock, said lock being movable to lock said driven means against movement in any of two pitch changing directions, and an electrical system comprising a feathering switch, a reversing switch, and a starting switch for disabling said governing means and simultaneously disengaging said lock to permit movement of said driven means in one of said directions.

l0. In an aircraft propeller comprising a hub, variable pitch blades carried by said hub, means rotatable with said hub for varying the pitch of said blades through positive and negative pitch' ranges including a source of power therefor, said source of power including elements energized by rotation of said hub, and a first controlling means for controlling said pitch varying means, the combination of, a locking member carried by said hub and engaging said blades for locking the latter against movement in one direction, means for governing said rst controlling means including a governor unit carried by xed aircraft structure, mechanism for interconnecting said governing means with the propeller hub including operative connections with said first controlling means, a servo system for said governing means including a servo output member operatively connected to said mechanism, a locking unit engageable with said output member for locking the latter in any of the pitch positions of said blades, auxiliary means operatively connected to said mechanism for energizing said elements when the propeller is stopped, and an electrical system comprising a plurality of manually operable switches, and a plurality of cooperating limit switches operable in response to predetermined positioning of said output member, at least one of said switches including connections for selectively operating said locking unit and at least one of said switches including connections for selectively operating said auxiliary means.

11. In a blade pitch changing system for an aircraft propeller including variable pitch blades, means for varying the pitch of the propeller blades, a source of power, means operatively connected to said source of power and said pitch varying means for controlling said pitch varying means, said pitch varying means being operable for positioning said blades over a plurality of pitch ranges in positive and negative directions, speed responsive means for governing said controlling means including a servomotor operatively connected to said controlling means and movable in two directions, and pitch stop means defining the extremities of said ranges including mechanism operatively connected to said control means for selectively locking said motor against movement in one of said directions while allowing it to move freely in the other direction in any of the pitch positions of said propeller including at least one element fixed against movement relative to said motor and operatively engageable therewith.

12. In a blade pitch changing system according to claim 11 including means operatively connected to said control means and said locking mechanism for locking said servomotor against movement in both said directions.

13. In a blade pitch changing system according to claim ll including ra source of power for operating said servomotor, and means responsive to a loss of power from said source operatively connected to said locking mechanism for locking said servomotor against movement in both said directions.

14. In an aircraft propeller comprising variable pitch blades, a pitch changing source of power,

means for varying the pitch of said blades in positive and negative positions and through a plurality of pitch ranges including operative connections to said blades and said source, a servomotor operatively connected to said pitch varying means and movable in two directions for operating said pitch varying means including a source of power for said servomotor, a controlling means operatively connected to said servomotor, speed responsive means for governing said controlling means, and limit means defining the extremities of said ranges comprising locking mechanism operatively connected to said servomotor and said controlling means, said locking mechanism being operable to selectively lock said servomotor against movement in one of said directions depending upon the direction of pitch change while allowing said motor to move freely in the other direction.

MELVIN E. LONGFELLOW.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,320,195 Rindfleisch May 25, 1943 2,424,559 Drake July 29, 1947 2,433,990 Hardy Jan. 6, 1948 2,476,063 Ridgley et al. July 12, 1949 FOREIGN PATENTS Number Country Date 560,522 Great Britain Apr. 6, 1944 

